The present invention relates to a sprag overrunning clutch and, more particularly, to an overrunning clutch which is automatically engaged or disengaged in response to the rotational speed at which it is driven.
Continuously variable transmissions (CVT) which have been proposed for use in the driveline of an automotive vehicle have typically involved the use of two variable V-belt pulleys joined by a flexible V-belt, each pulley having an adjusting device to vary the width of the pulley and thereby adjust the transmission ration, as shown in U.S. Pat. Nos. 4,630,504xe2x80x94Smirl and 6,050,911xe2x80x94Feuchter et al. Such transmissions have been effective, but are relatively inefficient and are complex and expensive to manufacture and maintain.
Alternative constructions for CVT transmissions utilizing overrunning clutches have been proposed to take advantage of the inherent high efficiency of such clutches as well as their simplified mechanical construction, thereby avoiding many of the disadvantages of the V-belt pulley transmissions.
U.S. Pat. No. 4,817,451xe2x80x94Weismann teaches a transmission employing roller clutches which includes an outer race spaced from an inner race, the inner race having cam surfaces which are inclined relative to the outer race. Rollers are set in a cage which generally rotates with the cam surfaces, such that slight rotation of the cage relative to the cam surfaces will result in selected engagement or disengagement of the inner and outer races through wedging or release of the rollers.
U.S. Pat. No. 5,145,042xe2x80x94MacPherson discloses a two-way roller clutch for use in a variable speed transmission which includes a cam disk having a plurality of elongated recesses formed in its peripheral surface and a roller retainer circumferentially supporting a plurality of spring-loaded rollers within respective recesses in the cam disk.
U.S. Pat. No. 5,263,906xe2x80x94Antonov shows an automatic transmission which includes a multiple disk type clutch which is controlled by pivotally mounted weights acting under the influence of centrifugal force.
U.S. Pat. No. 5,267,912xe2x80x94Casanova is drawn to a mechanical centrifugal clutch in which a drive shaft is connected to a planetary support which carries a plurality of weighted planetary gears meshed with a sun gear which is connected to a driven output shaft.
The present invention avoids the shortcomings of the prior known overrunning clutches by provision of a sprag-type overrunning clutch which is automatically engaged or disengaged smoothly in response to the rotational speed at which it is driven, rather than depending upon external activation.